Manufacture of artificial boards and like structures



o. w. FROST March 19, 1935.

' MANUFACTURE OF ARTIFICIAL BOARDS AND LIK STRUCTURES Fied Maron 2e,1932 l', gnap* VIII n mm, @mf

Patented Mar. 19, 1935 .l

UNITED STATES MANUFACTURE oF ARTIFICIAL BOARDS AND LIKE STRUCTURESOrcutt W. Frost, Cloquet, assignerto Wood Conversion Company, Cloquet,Minn., a

corporation of Delaware t Application March 26,

' 5 v Claims.

The present invention relatesv to fiber products,

such as insulation for heat and sound, and to artificial lumber, such asboards, shingles, and like forms which may be cut up, and to formed ormolded articles of various sizesV and shapes which may or may not be`suitable for size reduction. t

It has particular reference to the forming of board, or sheet materialof'- uniform thickness, that is with parallel surfaces, which can be cutinto various sizes and shapes for use as a substitute for sawn lumber.Such material is hereinafter referred to as sheet lumber.

Dense hard boards of the lprior art which are used as artificial lumber,or Wall board, and which are formed of wood ber, or other cellulosicmaterial, are ordinarily heavier and denser than ordinary sawn lumber.The latter averages about 30 lbs. per cu. ft. while the artificialboards referred to run from 40 to 50 lbs. per cu. ft., some vbeing wellknown which have a density of 1, or over 60 lbs. per cu. ft. Much of thematerial is so compressed and located that it is not efficiently used incarrying stresses. By the present invention, the material is soallocated in a structure that less dense, and stronger sheets may bemade from the'same amount of material.

An important feature ofthe invention as it is used in connection withsheet lumber, is the use.

of a core layer, and of one or two surfacing layers of suitablematerial. The invention incorporates in artificial fibrous products, theprinciple of mechanics which is effective in steel structures, such aschannel bars, angle bars, T-bars, H- beams, I-beams, andthe like,wherein: greatv strength is obtainable with a minimum of maerial.

In other words, in the present invention,- the material is so composed,and/or formed that it is most eiiicient where strength is required. Inparticular for sheet lumber, at least one strong surface layer isbacked' by askeleton structure have a skeleton connecting vto wet massesof the fibers, the mass itself acts 1992, ,serial No. 601,411

as a plastic body and dries into a unitary body. Sometimes a bindingagent is added, or one may be present in the ber mass, naturally, orformed therein by the process employed. From'experiments which I haveconducted I have shown that when the fibers of Wood, ligne-cellulose, orcellulose are hydrated by working mechanically in water, theself-cementing action of the fibers increases with the amount ofhydration. In this invention IY may employ such hydration processes toincrease ,the self-cementing .properties of a cellulosic material, `orVl may add a cementing agent, -or the cementing agent may be derivedfrom the fibers during the process.

The sheets made heretofore have employed a substantially uniform mixtureof base materials.

The sheets, or other shapes, have been made in sheet is thoroughly dry.The pressure applied y in part effects the density; A ysubstantiallyuniformity maybe obtained throughout the thickness of the sheet. Otherlsheets have been made with cessation -of heat andpressure, either oneor the other, or both, before complete drying of the sheet, so that theoutside surfaces have a different texture than the interior. Y

vOne defect of such` prior articles is Athe utilization of the samematerials on the entire interiorl of the board or sheet as is used onthe exterior. The requirements and the functions of the outer' layersand the inner layers are not the same, and the differences-are such thatthe inner layer in particular may be in part dispensed with, and mayincludecheaper material.

Another defect of prior art materials is th necessary density for therequired strength. Where 'thick boards are desired, too-much material iswastefully-used in the prior art processes and structures. -f

One object of the present invention is the provision of a board or likearticle having at the surface material suitable for `the requirements ofthe surface, and a less dense and a cheaper body supported and carriedby the material of the surface, said surface material extending into thebody and connecting the two surfaces.

Another object of the inventionv isthe provision of a skeleton core in aboard or like article. One particular object of the invention is theprovision of voids in the core of the article. I

Another particular object of the invention' is the of a compositestructure by' separately making (1) a core-forming base, and (2) one ortwo surface-forming bases, combining them after they have assumed someindependent form, and thereafter treating the composite structure toproducev a unitary, composite structure.

The present invention may be carried out in numerous ways, anddifferently appearing structures may result.. all of which, however,involve the fundamental idea of this invention.

Thick boards, like lumber, are frequently desirable, but the prior artprocesses of making thick boards are not economically adapted foroperation to effect this result. 'Thick boards are frequently desirable,because the transverse strength is proportional to the square of thethickness, and the surfaces bear the greatest stresses. Just as anI-beam becomes stronger by increasing the width of the web connectingthe flanges, so the board of the present invention becomes stronger byincreasingthe thickness of the skeleton core between the surfacelayers.- In making boardsvor sheet lumber, or like articles, by thepresent invention, I provide at least one sufficiently strong surfacelayer, but preferably two,` and a backing or connecting core ofsufiicient strength to support or carry the surface layer or layers, orthe stress layer, as it will hereinafter be referred to. In sheetlumber, two

parallel stress layers are carried and connected by a suitable core. Thegreatest variations in the invention as herein described are variationsin the character and formation of the core. Of course, a stress layermay vary widely in density, composition, and other properties, just asthe artificial sheets of the prior art may vary.

, In connection with the general and detailed description of methods,apparatus and products, which have been chosen to illustrate the presentinvention, the accompanying drawing is referred to. In the drawing:

Fig. 1 illustrates diagrammatically the arrangements of mechanicalelements which may be used lin carrying out the invention.

Fig. 2 represents an artificial board containing in the core particleslike sawdust as a filler.`

Fig. 3 represents a similar product containing in the core shreddedparticles, such as excelsior.

Fig. 4 represents an artificial board in which the filler comprisessystematically arranged solid elements such as wooden strips.

Fig. 5 represents an artificial board in which voids are formed byremoval of the elements present in the core during formation of theboard.

Fig. 6 represents an artificial board in which there is an intermediatelayer likea surface layer sandwiched between two core layers.

The materials for the stress layerrmay be the same as is used in anyprior art board, and may include fiber and a cement-ing agent. Thelatter may be added, or may be by nature an ingredient accompanying theoriginal fiber source, or may be onefformed incidentally orintentionally in the process of preparing the fiber. I prefer to use acellulosic iiber, and to treat it by a hydrating process to form acellulose hydrate. This may be a gelatinous film on some or all of thefibers, or it may be a liquid mass of completely gelatinized nbers'addedto less hydrated, or to unhydrated fibers.. I prefer. to use as the bodyof the fiber, a partially digested wood, or semi-chemical pulp, such asligno-cellulose, so termed to distinguish it from more completely cookedwood which is' substantially "cellulose in character. Where wood, ,orwood waste, or straw and the like as a raw material, is cookedwlthchemicals, lignocellulose is preferred to cellulose, because of thehigher yield of fiber to be obtained. Where ,hy-

dration is practiced to yform pulp-bonding material, eitherligne-cellulose or cellulose may be hydrated. If ground wood pulp, orother mechanically undigested wood, or other cellulosic material, isemployed, hydration of the cellulosic material may be effected,irrespective of the specific character of thecellulosic material.

As material for the core, any kind of pulp may layers, but the core as abody may have an4 average density which is less than the density of thestress layers.l The non-pulp part of the core may be void space, or anyfilling material eithervgranular or fibrous, and preferably, if fibrous,it is to be in the form of aggregates of fibers rather than fibratedmaterial. Flakes of paper, coarse sawdust, shreds of Wood, woodshavings, slivers of wood, and the like, may be used. Excelsior is mostdesirable because of its flexibility. A very coarse grade of suchexcelsior may be used. It is to'be understood that a pulp ce-v mentingagent is present in the lpulp part of the core to bind the pulp parttogether into a network, or a unit around a filler. Preferably, suchcementing agent is the same as is used 'in the pulp of stress layer, anda hydrated cellulose is suitable for both. By using the same bond in thepulp of the stress layer and in the pulp of the core an integralsubstance is established extend; ing as a skeleton or net workthroughout the unit, and it-may be made integral by the one process ofuniting and curing the different elements of the composite structure.

In practicing the invention the weaker core may be effected by creatingvoids therein, either systematically, as by some mechanicalrmeans, orheterogeneously, as by controlling the character of its composition. Inthe mechanical method I may incorporate solid material as a part of thestructure to define the voids and to resist and to transmitcompression,l and then remove the solid means, either bodily, infragments, or otherwise. I may use elongated rods or bars v'vhich may beremoved endwise from the voids formed thereby in the completed product.'I may use volatile or decomposable crystalline material, which remainsin solid form in the process, and remove it wholly or partly as a gas orvapor through the poresof the completed unit. I may use a leaveningagent in the core which may be either soluble or insoluble in water. i

While any solid may be used, such as sand, mineral fibers, animalfibers, and metal shreds or fibers, I prefer waste products, andespecially light-weight waste,-such as material which is less dense thanpulp parts. in their ultimate form. Coarse sawdust, shavings, orshredded wood, exemplified by coarse excelsior, are suitable lightweightmaterials.' The. more elongated is the form of such filler, the more itfunctions as a mechanical reinforcement. It is of such a character thatwhenvcompressed it forms interstices,

. which in the nal product are filled with cemented pulp integrallyunited to cemented pulp in the stress layers. p

To make such a board, I form a pulpy mass, preferably by treating woodwaste, in any way to form a wet fibrated mass. The flbration may bemechanical, chemical, or both. Ground wood may be used. Cellulose pulp,such as paper stock, may be used. Semi-chemical pulp may be used, suchas wood chips softened by a partial chemical digestion, and thenmechanically separated as in a rod mill. All or part of the pulp may betreated to form cellulose hydrate, as by the mechanical action of abeater (Hollander), a Claiiin, or a Jordan, or otherwise. A part of thepulp, or any other cellulose pulp, may be completely hydrated to agelatinous solution without fibrous form, or it may b e very highlyhydrated, and such cellulose hydrate may be added to less hydrated pulpor to unhydrated pulp. By any method, a self-cementing pulp mixture isformed, exemplified by a mixture of fibre, or pulp, and gelatinouscellulose hydrate. drated 'to form a gelatinous skin about each of them.Such material isa plastic mass when wet,

owing asa plastic mass.

The plastic mass described is used in part by itself to form wet pulplaps for the surface layers. It is also used `as the essential part ofthe core in admxture with the solid filler. For example 60% of` shreddedwood and 40% of self-cementing pulp (air dry weights) form a suitablecore. In practice three machines are used, one to form the wet mat ofcore, which may be about 2 inches thick, vand two others, such ascylinder machines, one above and one below the core former, for formingand discharging a wet lap of adhesive pulp onto the opposite surfaces ofthe wet core lap. The surfacing laps may be 1/8 inches thick when wet.The three laps are united, pressed through squeeze rolls to eliminatesurplus water, and then passed to a press. The process may becontinuous, or intermittent according to machines employed. Ifintermittent the formed sheets may be made initially of size suitablefor the press. If continuous, the composite sheet may be cut to fit thepress.

Multiple presses suitable `for the process are well-known and some mayoperate simultaneouslycupon as many as twenty such sheets. They arecapable of using pressures up to 1500 lbs. per sq. inch, and of beingheated by steam at a pressure up to 100 to 150 lbs. per sq. inch. Theymay also be electrically heated. A,

The pressure and temperature which may be employed generally arenotcritical in practicing this invention and may be varied according to theresults desired. For certain products fixed conditions may be specified.It is preferred -that the temperature should be sumcieht to boil out theexcess water. Air drying or evaporation is l vnot excluded, however, andit may be ldesirable for .certain special types. It has been found thatthe air-dried product is better when hydrated cellulose is present, asthe'concentration of the hydrated or gelati-nized cellulose isincreased. The

inch and a mechanical pressure .of 250 lbs. is san- 'isfactory for V,ageneral purpose sheet lumber.

When pressure and a boiling temperature are applied, the applicationsarepreferably simultane- Preferably all the bers are hyous, andarecontinued until liquid water in the mass has been boiled out. Suchdrying converts the cellulose hydrate into a hardhorny mass which -isintegral as a continuous masser net. work from face, through coretofacefbeing substantially uniform in` character through its indensityfrom face to face, with the 'same pulp maSS.

Breaking point f d. t under Poun s ransversc bonded Composi- Thck'Pounds load Item pulp r on ness face per cu. applied Sq. to Iacex tt atcenter of 6 in. span 4 inches wide Per cent l 635 pulp... .137 in. 43. 546. 7 lbs. 2 432 55pulp...

. 45 shred-- .260 in. 31.0 85. 5 lbs.

wood 3 573 45 pulp v o5 Shred-- 553 in. 2,5. 6 135.0 lbs.

The foregoing tableclearly demonstrates that a less dense boardcontaining a less quantity of bonded pulp, may be stronger' than thesame area of board containing more of such pulp.

As a detailed example of carrying out the indischarged and may becouched over to aV conveyer belt, preferably in the form of a screen 12,under which there is a suction box 13. The mat is thus made more denseand less wet.

Additional felting means, such as Olivers l5y above the mat 11 and 16below the mat il, form thinner sheets or mats l'l and 18 of pulp,preferably identical with that used in adrniuzturer with the sawdust.lThese laps are couched to conveyer belts 19 and 20 to bring.,them-toward the core-mat 11, at which they are properly directed to formfacings on the core mat. The

three mats move uniformly together as one sheet 21 over a. conveyer 22,preferably a screen, to squeeze rolls 23for removal of surplus water,and for a uniting compression of the mats. The sheet may then be outintosizes ksuitable for the hot press. In the press vthey may besubjeced to a continuous pressure of 250 pounds per' square inch, and adrying heat produced by a '10 pound steam pressure within the platens ofthe press.

Fig. 2 represents the product in cross-section.

The product has three zones 25, 26 and 21, `of which 26 is the core. 27are substantially pulp layers, and the pulp substance extends from onelayer to the ,other,l

The surface zones 25 and f through the core as an integral substance,designated in the core as 28. The parts 29 designate the sawdust, andrepresent generally whatever fller may be used. One surface layer in thepress may be formed against a wire screen on the platen, as is wellknown, for aiding the liberation of steam in the drying process. Screenmarkings 30 are designated.

In `the manufacture above described it is not necessary to form twostress layers. The lower Oliver 16 and its product 18 may be omitted,and to some extent a less denite stress layer having a uniform surface,will be formed by gravity drainageof the pulp substance to the lowerside of the unit.L The ultimate essential characteristics will howeverprevail in the resulting product Where a water-proofed product isdesired the surface layers 1'7 and 18 may be suitably treated or sized,either in the pulp form before felting, or after felting, as desired.When such treatment is limited to the pulp in the stress layers only,there is economy in sizingA materials as compared to sizing all the pulpfor the board, as practiced heretofore forthe uniform type of In Fig. 3a similar product is 'shown in which vshreds of wood such as jexcelsior32 is present in the core, contained in the hardened intejral matrix 33which is comprised in the surface layers and which fills the intersticesbetween the shreds.

Fig. 4 represents a departure from the forms of Figs. 2 and 3, in whichthe filler is systematically arranged. Wooden strips 35 of triangularcross-section are arrangedin complementary relation as shown. 'Ilhesemay be left embedded in the product. The pulp 36 extends integrally fromface layer 37 to face layer 38, and between 'the adjacent lengths offiller in the form of webs 39. In manufacture various expedients may beadopted for incorporating'the filler. It is to be noted that prior tocompression in the press, the adjacent lengths may be more separatedalong the line of the thickness of the board, and in the process ofcompression the faces 40 and 415 aid in compressing the pulp in theweb.

In Fig. 5 a further modification is shown, similar in original form tothat of Fig. 4. Rods auch as round metal rods 42 may be inserted in thecore base and housed therein as the filler.

' They may `thereafter be withdrawn, leaving voids indicated as 43 inthe core, to reduce its average density. Thus the entire substance 44 ofthe core and the stress layer is the same, is integral, and of the samedensity, but because of the voids, the average, density of the core isless. Likewise, strips shaped as in Fig.- 4 may be withdrawn, and theymay be originally supr-pliedas metal -rods,.as in Fig. 5 for the purpose'of easy withdrawal. The contraction of metal on cooling contributestothe separation of the rods from the pulpv in the core.

'In'Fig. 6 it i`s shown that the'invention is not limited to unlledlayers at the surface. Such layers may be arranged within the core inone or more layers, exemplified by asingle layer of pulp 46 sandwiched-between two core layers 47 and 48,the whole being integrally united by-the pulp substance with two surface layers 49 and 50 ofl pulp base. Y jIn general discussion it may be stated that the sawdust particles,` andthe shredded wood of Figs. 2 and 3, respectively, are not necessarilycemented to the pulp substance, and may Ibe vsqueezed therefrom into thesurface layers lvoid. 'I'hey function in the process of forming aspressure-distributing means and as means for forming voids in theintegral substance. Because of the cheap character ofthe filler, it maybe left in the voids which it creates, and it is not detrimental to thedesired character of the product if the filler particle draws away fromand resides more or less loosely or detached in the void. The forms ofFigs. 2 and 3 are the preferred forms for reasons of simplicity andeconomy in the process of manufacture.

'I'he product may exhibit a characteristic laminated structure in theplanel of -the sheet at any part of thel body, but this is to bedistinguished from the existence of separable and distinct layers. notcubical such laminations may readily occur to the extent that thefibers, or the filler, are elongated in character. y l

In generaldiscussion of the process of formation, it may be stated thatmechanical pres- Because the compression is unilateral and each otherand to the horny cement. Likewise,

high temperature is not essential to the formation of the'hard and hornymass from hydrated cellulose. It is material to the speed of drying. Thetransfer of heat to the-interior is quicker by higher heat. In the caseof metal inserts the transfer of heat to the interior is quicker than inthe case of less conductive filler in the core, such as wood, sawdust,shavings, shredded wood.4 The ,latter absorb some water, and this alsomust be driven oif as well as the water in the selfcementing pulp.

'I'he invention is not limited to any particular-thickness'of the stresslayers, or the core, or any particular ratio of thicknesses. A very thinface layer may be used, and some decorative features may result inregulating thicknesses. For example, when the stress layers aresufliciently thin, the pressure means in the core, whether rods, grids,sawdust, shredded wood, or whatever may be used, can be made to exhibitshadowy or clear-cut markings in the exposed face, due to slightdeviations `from equal distribution of preure. Particularly withshredded wood a variegated net work of lines may appear having slightlydarker shade where lengths of `shredded wood press against-the surfacelayer.

Colors may be incorporated into the surface layer, and may also, ifdesired, be incorporated into the shredded wood to be preferentiallay ocause a mottled design in' color. f

'I'he chips o r other filler may be previously coated with awater-excluding substance, or otherwise treatedto prevent uselessabsorption of water from the aqueous pulp. Parafiln may be used, andwill so function until heat is applied. Upon application of' heat thelparain will melt and it is then distributed throughout the board bydiffusion, making the -nal product more water-resiaant. I have foundthat paraffin and any similarly acting material increases the dryingtime because of the subsequent diffusion under heat. 'Howeven when 'asuitably heat-resistant substance like gilsonite is used to render thefiller water-resistant,- the time of drying may be shortened, becausethere is no water in the filler to be removed.

The product may be made with the particular object of providing highthermal insulation properties. The less dense is the board,'tl1e moreair spaceA there is within itand hence the more` eiective it is as aheat insulation. The forms which have large voids therein, such asunfilled air spaces, .and the more spongy forms, are particularlyadvantageous as heat insulation. It is also to be understood that thesound transmitting property is lessened, and the sound absorbing qualityis increased, by the same factors which increase the heat insulatingcapacity. In other words, the acoustical and the4 thermal properties maybe advantageously increased by decreasing the averageI density of theproduct.

Products of the present invention may be made to approximateflumber inphysical characteristics, and may or may not be grained to some degree,according to the character of the filler. It has greater strength perunit weight than the boards of uniformly dense material. Because ofl theuse of filler as described, the product may be made in thicker form withless problems incidental to dryingthan are met with in making boards ofthe same thickness yfrom uniformly homogeneous pulp masses. The

boards are cheaper to make per unit of thickness. 'I'here is lesswarping, expansion and contraction because of the lower average densityof the core. The board will receive and'will hold nails at the edges,without splitting. The product has a higher thermal insulating valuethan the denser forms. It may have an attractive surface appearancesubject to variation by slight changes in proportions and in materialsemployed in the process of construction. When sizing is desired,reconomies may be effected.

It is also to be understood that sizing vand water-proofing agents maybe incorporated-.finto any of the laps for the surface, or the core.Materials for such purpose are well known. The fibers employed may beproofed against water,

fire, insects, and rot in any known manner, if

desired, and such other changes and modifications, and prior artpractices may be adopted, without departing from the invention asexpressed in the appended claims.

I claim: f

1. The method of makingan artificial boardlike product which comprisesmaking a wet core by forming around particles of a filler a skeletonnetwork of wet brous composition capable of a self-cementing action ondrying, forming on said core a wetl surfacing layer consistinglsubstantially entirely of fibrous composition having cementingproperties similar to the fibrous composition of the core, pressing thecore and surface layer together, drying the resulting body into anintegral unit, andremoving the filler to leave voids in said coreportion of the unit. 2. The method of making an articial boardlikeproduct which comprises making a wet corev by forming around elongatedrod-like elements a wet fibrous composition capable of a self-cementingaction on drying, forming on said core a wet surfacing layer consistingsubstantially enltirely of fibrous composition having cementingproperties similar vto the brous composition of the'core, pressing thecore and surface layer together, drying the resulting body into anintegral unit, and removing .the rod-like elements from the core.-

3.,'1'11@ method of making an artificial boardf like productwhichcomprises making a core by.y

forming around ller elements a skeleton network of a self-cementing massof structural composition, forming on said core 'a surfacing layerconsisting substantially entirely of the essential composition of saidcore, treating the united core and layer to cause setting and integralunion of said core and layer by its self-cementing action, and removingthe filler elements.

4. The method of making an artificial boardlike product which'comprisesmaking a core by forming around filler elements a skeleton network offiber and cementing bond, forming on said core a surfacinglayerconsisting substantially entirely i of ber and a cementing bondhaving cementing I Aa surfacing layer consisting substantially entirelyof highly hydrated cellulose and fibers. treating oacUTr W. FROST. I

